This invention relates to a new glycyrrhizin isomer, a composition containing such isomer and the method for manufacture thereof.
Glycyrrhizin, as used herein to denote glycyrrhizinic acid or a salt thereof, is a well-known substance as effective ingredient of Licorice used heretofore as medicine or sweetener. At present, isolated and refined glycyrrhizin is used widely in many fields of application and, especially, free acids, as well as sodium, potassium and ammonium salts including acidic salts of glycyrrhizin are used most widely or studied for their properties, all of these substances exhibiting marked sweetness and various pharmaceutical activities. While potassium and sodium salts are fairly soluble in water, ammonium salts and free acid are soluble only difficultly in water. When dissolved in hot water to an elevated concentration, glycyrrhizin is gelled after cooling the solution, while the aqueous solution leads to gel formation when made acidic. The aqueous solution shows bubbling properties and the bubbles, once generated, do not vanish over an extended time interval.
The chemical structure, including steric structure, of such glycyrrhizin has been clarified and, in the case of a free acid, the structure is that of a glycoside of triterpene as shown by the formula, ##STR2## (3.beta.,18.beta.,20.beta.)-20-carboxy-11-oxo-30-norolean-12-ene-3-yl-2-O- . beta.-D-glucopyranosiduronic-acid
(C.sub.42 H.sub.62 O.sub.16, molecular weight=822.92).
As may be inferred from the above formula, glycyrrhizin may have several steric isomers. However, heretofore, every glycyrrhizin isolated from Licorice unexceptionally has the above formula and no steric isomer of glycyrrhizin has been isolated from plants other than Licorice. It is naturally not clear whether theoretically possible isomers have the same properties as the above glycyrrhizin derived from Licorice and, heretofore, only the substance having the above steric structure was denoted by the term glycyrrhizin.
The present inventors have discovered, after a continued research in the field of glycyrrhizin, that a product obtained upon prolonged alkali treatment of glycyrrhizin has, as solution, markedly different properties from the starting glycyrrhizin despite the fact that no chemical changes seem to have taken place, and that such different properties may be ascribable to the formation of a steric isomer of glycyrrhizin, and completed the present invention.
The new isomer isolated by the present inventors from an alkali treated product of glycyrrhizin, is different from ordinary glycyrrhizin only in that the hydrogen atom at the 18-position has an .alpha. steric configuration. In the present specification, this new isomer is designated 18 .alpha.- for distinction from ordinary glycyrrhizin designated 18 .beta.-. The 18 .alpha.-isomer thus has the following structure. ##STR3##
While showing some properties in common to 18 .beta.-glycyrrhizin, 18 .alpha.-glycyrrhizin shows such peculiar properties as may not be expected from its small structural difference consisting in the different steric configuration of only one hydrogen atom.